Articles made of vitreous materials which contain heavy metals, such as lead, barium, cadmium, etc., are desirable for their attractive appearance. Frequently, high quality foods and beverages are sold and stored in decanters formed of crystal or a lead-containing glass. As used herein, a lead containing glass means a glass containing lead oxide, PbO, and unless otherwise indicated, percent PbO or percent lead indicate weight percent PbO. For a lead glass to be classified as crystal, it must contain at least 24% by weight lead oxide, and preferably contains at least 30% lead oxide. (See Norme Francaise, NF B 30-004, December 1971, established by the Association Francaise De Normalization, AFNOR. Glass having greater than 24% PbO w/w is classified as "cristal au plomb," and glass having greater than 30% PbO is classified as "cristal superieur.")
Articles formed of crystal are desirable because of the pleasing aesthetic appearance which the lead in the glass lends to the article. Frequently, crystal or lead glass flasks are used to store high quality alcohols, such as cognac, whisky, and wines, as well as fruit juices and aggressive, pasty products, such as mustards and other acid containing foodstuffs (as used herein, the term liquid refers to both pastes and liquids). It is well-known that any liquid stored in a container or receptacle has a tendency to dissolve some quantity of the chemical constituents of the materials forming the container. The quantity of material forming the container which is dissolved or leached into the liquid stored in the container is generally extremely low. For example, water stored in a container of sodocalcic glass will solubilize some Na.sub.2 O from the glass. Standard tests (e.g., Deutsche Industrie Normon, DIN, 12111, January, 1962) are available which provide a comparison of the hydrolytic resistance of sodocalcic glasses (water will dissolve 30 to 1000 .mu.g Na.sub.2 O per gram of glass exposed thereto for a duration of 1 hour at 90.degree. C.).
The general phenomenon of leaching of container materials into liquids stored in the container is often considered to be of significance in analytical chemistry and in academic research, but this leaching tendency is generally not considered significant in everyday use. However, when materials, such as spirits and acid foodstuffs, are stored in articles made of vitreous materials containing heavy metals, there is a tendency for some heavy metals, such as lead, barium, and/or cadmium to migrate or leach into the foodstuffs stored in the container. Even a material having a relatively moderate acidic pH (e.g., pH=3.5) will leach a substantial amount of lead in a relatively short time period, and leaching will increase with time.
In fact, serious studies have led to international regulation standards "in order to ensure the protection of the population against possible dangers due to the contact between foodstuffs with the surface of articles made of glass used for the preparation, the service and the conservation of foods and beverages" (See International Standard ISO 7086/1-1982, established by the International Organization For Standardization, ISO, Geneva, Switzerland).
In particular, higher quality spirits are stored in crystal flasks containing a high percentage of lead oxide. In some countries, the health control authorities have strongly recommended a maximum lead content for alcoholic beverages, which has an impact on the producers of crystal flasks used for high value alcohol storage. Since high value spirits are often stored in crystal flasks containing a high percentage of lead, and since these spirits are stored for long periods of time in such flasks, a substantial amount of lead can leach or migrate into the alcohol which is ultimately consumed. For example, in the United States, the state of California, Safe Drinking Water and Toxics Enforcement Act of 1986 (known as Proposition 65) requires warning labels on lead glass containers if they are susceptible to leaching unsafe quantities of lead into food and/or beverages stored therein.
Applicant has disclosed in U.S. Pat. Nos. 4,981,733 and 4,983,199 that the problem of metal leaching can be solved by forming a crystal container which has on its internal surface a thin and continuous film made of unleaded glass; this thin layer of unleaded or low lead glass forms a screen against leaching or migration of heavy metals from the crystal into any product or drink stored in the container. The process for forming these metal-leaching-safe crystal flasks, involves (1) gathering a quantity of flowable unleaded glass into a drop shape; (2) gathering a parison of crystal over the aforesaid unleaded glass so as to cover the unleaded glass (the unleaded glass and crystal having similar coefficients of expansion and indices of refraction); and (3) blowing the crystal and unleaded glass together to form a desired container configuration, which has a cavity with an internal surface covered with a continuous film of unleaded glass.
While the foregoing solution allows for the safe storage of spirits and acid containing materials in a lead glass or crystal container, it is difficult to carry out the foregoing process and difficult to ensure that a continuous film of unleaded glass is provided on the surfaces of the resulting article that will come in contact with stored materials. It is also difficult to produce a thin and continuous unleaded glass layer on the interior surface of a lead glass flask. Using the existing processes, if one tries to produce too thin an unleaded glass layer on a leaded glass, the layer may not be continuous, and will therefore leach lead into materials contacting the incompletely coated layer.
Therefore, it is desired to produce crystal or leaded glass articles having an internal surface which can come into contact with acid containing materials or alcohols and leach only a minimal quantity of heavy metal into said materials. It is also desired to produce lead glass containers which have minimal lead leaching characteristics by a new and simplified process.
Therefore, it is an object of the present invention to produce an article of crystal or lead glass which prevents migration of the lead contained in the crystal or lead glass into an acid product contained in the article.
It is a further object of the present invention to produce an article made of crystal or lead glass having a continuous, thin layer on the surfaces of said article which come into contact with materials stored in said container, said layer being capable of minimizing or reducing the migration of lead from said crystal into the material stored in the container.
It is yet another object of the present invention to produce an article of crystal or lead glass which prevents migration of the lead contained in said crystal or lead glass into an acid product or alcohol contained in said article by a simple process.